Methods of and apparatus for rendering visible magnetic and electric field patterns



METHODS OF AND APPARATUS FOR RENDERING VISIBLE MAGNETIC AND ELECTRIC FIELD PATTERNS Filed Sept. 24, 1951 T, 2 Sheets-Sheet 1 June 17, 1 958 G FRIES I 839,601

I n ventor GUS TAVB FR 4E5 M v 7" W) A tlorney June 17, 1958 FR|Es v 2,839,601

METHODSVOF AND APPARATUS FOR RENDERING VISIBLE MAGNETIC AND ELECTRIC FIELD PATTERNS Filed Sept. 24, 1951 2 Shpets-Sheet 2 GUSTAV rams I My, MSMJU Attorney mum METHODS on AND APPARATUS FOR RENDER- ING vIsrnLE MAGNETIC AND ELECTRIC FIELD PATTERNS 1 Gustav Fries, Ostheim, 'Kreis Hanan (Main), Germany, assignor to Julius Cato Vredenburg-Inglesby, London, England Application September 24, 1951, Serial No, 248,064

Claims priority, application Germany September 27, 1950 6 Claims. (Cl. ;178-6.6)

luminous effect produced by a flow of electrons in a tube filled with mercury vapour. However, in order'to're'nder the pattern of a magnetic field visible by thefseinetliods, relatively powerful magnets are required. 1

Another method, which likewise became known in the U. S. A. in 1949, is based upon .the' electromagnetic shadow effect. According to this method there is superimposed in an electron microscope upon the electron shadow of, for example, a wire magnetised with speech frequencies by means of a magneto'ac'oustic device, the

electron shadow of a fine wire net, and thereby distortions of the shadow image of the wire'net are producedjthe meshes of which are otherwise regular (periodical Uinschau published by Umscha'u-Verla'g, Frankfurton-Main, Germany No; 5, 1950, page 155)., This method can only be carried out in a high vacuum'and' supplies black-and-white images. It is an object of the present invention to'render mag netic fields or electric charge patterns visible" without it being necessary for these fields to be strong or forithe carrier of the magnetism to be placed in a high vacuum; another object is to reproduce magnetic fields ofditferent strength or electric charges of different potential by gradnation in brightness according to'their value. 1

According to this invention the magnetic 'or electric charge pattern are placed in the proximity of an electronfields emitting'surfac'e, for example, of a photo-cathode. It has been found that in this manner the electron emission of said surface is modified in accordance withthe pattern of the magnetic field distributionor the electric charge pattern, thus transforming the same intoan-electron image which can be rendered visible in' variousways 'well'kncwnto those skilled in the art; ,Accordingto a preliminary explanation, in this manner the energy required forreleasing electrons from the photo. cathode-is influenced or'controlled, and accordingly if ,theelectron image produced on the photo cathode is emitted, ac-

celerated andgfocused' upon a luminous screen by .an'

elect'ron-o'ptical device, the pattern ofthewmagnetic fields or electric charges becomes visible." on this; luminous screen; i In order thatthe invention may be more readily understood, various aspects and embodiments will now be de scribed with reference to the accompanying drawing.

Figs. 1 and 3 illustrate one form-of apparatus, Fig. 1 being a back elevation showing only certain elements, including the luminous screen,

Fig. 2 is a somewhat diagrammatic view, partly in perspective. and partly in sectional-elevation, While 7 Fig. 3 is a front elevation taken on section line A A ofFig. 1, showing certain'elements only,

Figs. 4-8 are representations of the luminous screen under difierent conditions,

Fig. 9 is a somewhat diagrammatic side elevation of a 7 form of apparatus suitable for transforming magnetic oscillations into oscillations of light,

Fig. 10 is a diagrammatic perspective view, partly in section, of one form of apparatus for producing on a strip-like carrier cinematographic series of magnetic-records of two-dimensional optical phenomena.

Fig. 11 is a schematic section on line C'D of Fig. 10,

Figs. 12 and 13 show,'in two elevations at right angles to each other, a detail of the apparatus of Fig. 10.

Fig. 14 shows diagrammatically a form of. apparatus for reconverting cinematographic series of field-pattern brother picture records into visible cinematographic pictures, and

FigQlS is a sectionon line E-F of Fig. 14.

Referring now first to Figs. 1 to 4. The bundle of vessel upon a metallayer semi-transparent to light.

lf'a'line grid '7 and, for example, a steel band 8, are in- I s p terposed in the path of the light beam 5 between the lens- .14 and the photo cathode 6,anelectron-opticalshadow image 13 (Fig. l) is produced upon the luminous screen 11 when the electron-optical device 10 is electric voltage from the source 12.

it now, for example, a permanent magnet 14 is placed uponthesteel band 3 with its poles l5 and 16 bridged by supplied with the steelv band,:the latter becomes locally magnetise'd.

When the. band is brought before the photo cathode 6,

I vthe magnetic field recorded at this point on the steel band 8 then influences the energy required for releasing the electrons leaving the photo cathode 6 so that an electronic image corresponding to Fig. 4 becomes visible upon the luminous screen 11. I

A This method may be'modified by also activating that part. of the photo cathode 6 which issituated in the-op- ,tical shadow of the steel band 8 when he latter 'isillumifnated by the beam of lights. For this purpose a source of light 17 may be provided which illuminates the photo cathode 6 from its back'through optical means 18. Since now the shadow 13 of the steel band 8 (Figs. 1 and*4).' is illuminated, the image obtained on the luminous screen (Fig. 4) is modified correspondingly into an image as shown in Fig. 5. In this the shadow l3of the steel band 8 is no longer visible, and the image now only constitutes the cathode image of the pattern of the magnetic field. It can'be verified by the image obtained that by stroking the steel band 8 with a permanent magnet 14, the

previous magnetic impression can again: be erased. IIt. is true that in this case magnetic lines of force can still be foundat the two ends of the-band 8. However, the

band'can also be entirely de-magnetised by meansof the permanent rnagnet' 14 if the magnet is approached and removed-step by step while being moved overflthe band;

as can be demonstrated by means of the apparatus shown inFig.,2 V "e vvThisform of apparatus therefore constitutes a useful meansfor demonstrating. and, examining magnetic phenomena.

Another. application" of particularly great practical im-. vportance is illustrated in Fig. 9, in which, for example,

the recording head 19 of a magnetic recorder is arranged the recording head. faces the photo cathode.

cording head 19 (Fig. 9) whennot talked at, while the image surface into 1000 lines, would Fig. 6 shows the shadow image of the recording head 19 when talked at. It can be seen how the magnetic field at the location of the gap builds up and collapses. If the photo cathode 6 is additionally illuminated by the source of light 17 through optical means 18, then the image on the luminous screen assumes the form shown in Fig. 8. Since the recording head 19 is supplied with alternating currents, these images on the luminous screen change periodically in accordance with the frequency of the current and therefore are advantageously observed through astroboscope mirror, thus resolving the generation and disappearance of the image of the magnetic alternating field into part-images, but preferably the whole phenomenon is cinematographically recorded in the manner of slow-motion pictures.

By. themethod and apparatus described not only magnetic fields but also electrostatic fields can be rendered visible. If, for example, a suitable carrier 8 to which electric charges have been applied is placed in front of the photo cathode 6 instead of a steel band, the location of the electric charges on the carrier becomes also visible upon the luminous screen 11.

In this manner recordings obtained by the method of Electrography (Zeitschrift fuer Technische Physik, volume 16, issue 12, 1935, pages 607-614) may be rendered visible.

A further feature of the present invention consistsin accelerating the whole photo cathode image to such an extent that it leaves the high Vacuum. in the form of cathode rays through a Lenard window (similar to the. window 26 hereinafter described with reference to Figu're 10) so as to strike and charges electrically the whole of an image surface on a carrier film of insulating .material which is placed outside the Lenard window.

Since, however, an electric charge image normally does not adhere for long in the atmosphere, according to another feature of the invention an image'recording is effected by magnetising a magnetisable layer applied upon a carrier.

Fig. 10 shows one form of suitable apparatus for the recording of moving pictures upon a magnetisable carrier 42, while Fig. 14 shows one form of apparatus for reproducing such magnetic image recordings. The latter apparatus can also be employed for the large-screen projection of photographic moving pictures and of'television pictures. The recording of the moving pictures as shown in Figure 10 is effected by causing the lens 21 to form upon the photo cathode 22 a stationary image of the scene to be recorded, thus producing an r electron image on the photo cathode. This electron image is accelerated from the photo cathode 22 by the anode 23 having positive electric bias and is focused upon this anode with high definition by a coil 24 which acts as a magnetic lens.

image and such a fraction of its height'as corresponds to the number of lines into whichit is intended for the The anode 23 itself is provided with a slot-like opening 25 which has the width of the image to be dissected. Assuming, in accordance withi has a'width of 88 mm. and a height of 76mm then the height of the opening 26, assuming dissection-of 0.076 mm. 7 Z

The electron image comingfr'o'm'the photo'cathode 22 is further swept in saw-tooth fashion torm'ove vertically past the slot opening 26 of the anode. 23 bya pair have to be of deflector coils 29 and 30 (shown in broken'lines) which is supplied with a saw-tooth sweep current from an electric battery 32 through a rotating potentiometer 31.

image pass line by line through the slot opening and In this manner periodically parts of the electron 'lector anodes 35 provided behind the anode 34 in multiple arrangement. (In order not to complicate the drawing, only ten collector anodes 35 are shown in Fig. 10.) These collector anodes 35' are distributed over the width of the line and subdivide the line into image points. In the assumed example of dissection of an image into 1000 lines with 76 mm. image height, on the width of the line of 88 mm. with a spacing of 0.01 mm. roughly 1158 collector anodes of this kind would have to be provided so that the number of the points into which the image area could be resolved would be 1,158,000. Since, however, in cinematography and tele-' netic qualities.

" The electrons impinging upon the collector anodes 35 control amplifier tubes 36 and 37 associated with each collector anode (only two have been illustrated in the example). The anode current of these tubes is thus modified with the brightness value of the image points, and its A. C. component is conducted through condensers 38 'and'39 to recording magnets 40, 41, etc. These magnets are placed side by side in a line and are in contact 'with the carrier 42 to be magnetised.

Since each of these recording magnets has only to record one point on the image line, it has to deal, in the 1000-lines example, a'fr'equency of 1000 per image or, in the case of 25 images per second, with a frequency of 25 kc. per second, a frequency which is well within the range of possibility and can readily be accommodated on a carrier length of 45.6 cm. It-is thus possible for a carrier film'having a layer of magnetisable material in the size of the usual 35 mm. standard cinema film to be used for the image recording. Fora 1000-line resolution of the image field of 19 x 22 mm. with standard film size there is only, for the time being, the difficulty of accommodating in a line 22 mm. long as many as 1,158 recording magnets side by side, as is shown in Fig. 13. In this case each magnet, assuming an anti-magnetic spacing layer of only 1000th of a mm., would be roughly 0.018'mm. wide.

Practical experiments of magnetic image recording according to the invention have,- however, already been carried out successfully with lower numbers of image points. Infthese the image size upon the carrier band of 35 mm. width was 19 x 22 mm. and on a line there were 40 magnets arranged side by side with interposed anti-magnetic spacing layers of 0.05 mm., so that the image resolution with squarearrangement' of points was 38 X40=1,520 points. This in fact is already more than was usual in the first television transmissions in 1930.

It-rernains to be described on the recording side how 'therm'agnetisable carrier is moved past the recording head 40, 41, etc. The carrier 42 is arranged ina known manthe normal speed of 45 .6 cm. per second corresponding to 25 frames per second. Accordingly the slide contact through a secondanode 34 at a higher voltage, which is likewise provided witha slot 33, to strike upon col- S1 of the potentiometer 31 is driven by a gear wheel through a pinion 52 and thus produces the required sweep current for the pair of coils 29 and 30 synchronously with the frame change and with the continuous movement of the carrier. As a. result the electron image, and consequently the magnetic image being recorded, will be stationary, during each framesweep period, relative to the moving. carrier, on which it will thus be recorded progressively as the carrier moves past the recording magnets. Then during the fi'y-back period of the sweep the electron image is. moved back so as to advance on the carrier by the length of a frame. Fig. 11 is a section on: line C-D, Fig. 10, of the electron image tube 53.

Simultaneously with the magnetic recording of the image, the magnetic recording of the sound upon lhe carrier 42 is effected through a microphone 54', amplifier 55 and magnetic recording head 56, so that, immediately a after recording, both the image and the sound are adapted to be reproduced. This possibility is of particular importance in sound film studios for the instantaneous checking of picture and sound after shooting. It also provides a method of rapid transmission for television reporting, for example, when it is necessary for the reporting to be stored temporarly while the transmitter is radiating some other transmission.

Apparatus suitable for the reproduction and largescreen projection of the magnetically or electro-statically recorded images is illustrated by way of example in Fig. 14. In this case the carrier 57 upon which the recording has been made, for example, an electrostatic image and sound recording, is continuously withdrawn from the supply spool 68 via rollers 59 and 60 by means of the toothed drum 53. In this movement the carrier 57 passes at a uniform speed a photo cathode 61, which is illuminated from the inner side by a source of light 62 through lens system 63 and is thereby caused to emit electrons. is so large as to be simultaneously influenced by two electrostatic images 64 and 65. The two electron images produced in this manner are accelerated towards and focussed through an electrostatic optical device 67 upon a layer 164, which is adapted for secondary emission and which is applied upon a thin metal partition wall 25 which, similarly to a Lenard window, is pervious to accelerated electrons. The metal film 25 need not, however, be supported by a grid as in the case of a Lenard window, since it is located wholly within the high vacuum space of the tube 162: and therefore is not exposed to unilateral pressure. The focus coil 70 causes the electron image or secondary electron image coming from 164 to be directed with sharp definition and without diffusion, in a second stage, upon a further emission layer 71, which is provided on a further metal skin 72 biased with a higher voltage than the metal skin 164 so that the electron image is once more accelerated on its way to layer 71. In a third stage, i. e. between emissive screens 72 and 73, electron-optical equalisation is effected in the form of a saw-tooth periodic sweep to compensate for the image movement due to the movement of the carrier 57 and thus obtain a further image 88 which is now stationary. To this end, while the electron image coming from the screen 72 is once more projected with sharp definition upon the metal film constituting screen 73 by means of the focus coil 75, at the same time the electron image representing two consecutive images placed above one another, is periodically swept upwardly by means of a saw-tooth sweep current supplied to the deflector coils 76 and 77 (see also Fig. 15, which is a section on line EF of Fig. 14), synchronously with the movement of the image carrier 57 in such manner that the image 88 appears stationary at the middle of the screen 73.

the carrier takes to move forward by one frame pitch, so that after this period the next following frame on the carrier will be projected, thus producing the well known cinematograph effect. The sweep current is supplied to the deflector coils 7'6 and 77 from a battery 80 through the sliding contact 78 of a potentiometer 79 which rotates The photo-electric layer of the photo cathode The length of each sweep period is equal to the time which synchronously with; the movement of theimage carrier. The sliding contact 78 itself is. driven; similarly as in the recording apparatuslFig. 10), through a gear wheel 81 and pinion 82, from the toothed drum 58, which itselfis driven by motor '83 through a worm drive 84, 85. v I

This electron-optical equalisation of the movement of the two images 64 and 65 which are positioned above one another and which come from the moving image carrier 57 (see also Fig. 15) in relation to astation'ary image upon 73, is an important feature of the invention. This equalisation is in principle also applicable during recording when for example the electron images are ap' pliedto a continuouslymoving image carrier as electric charge images without raster. The advantage of an electron-optical equalisation of the image movement as compared with mechanical equalisation (Mechau cine-projector) consists in the fact that an electron-optical sweep can be effected with-out inertia and extends upon the image line, whereas in the case of purely optical equalisation three images are required which in reproduction mustibe superimposed by mechanical means,

-Now after the image field 88 of the electron image coming from 71 has been rendered stationary uponthe emission electrode 73,. it can; in a subsequent stage be accelerated once more towards, and focussed by a coil 7 89 on to, aluminous screen90 where is transformed by the impact of the electronsupon the screen into a light image adapted to be projected by a lens system 74.

The reproduction of the sound associated with thesequence of images is efiiectedjin known manner, the sound track being scanned on the carrier '57 by means head 91, the output currentof which is amplified inaniplifier 92 and radiated as sound through loudspeaker 93.

The focus coils 70, 75 and 89, which are adjustably supplied with current from sources '94, 95 and '96 through the resistances. 97, 98, 99, may be replaced by annular permanent magnets when an apparatus according to Fig. 14 has become standardised. In this case the sources of current with accessories become redundant.

The apparatus according to Fig. 14 is' als-o adapted for the projection of normal cinema films. In this case the photographic image film 102 is moved past the objective 163 and the illuminated image upon the film is projected through the objective 163 with sharp definition upon the photo cathode 61 where it is converted into an electron image, and the image amplifying and projecting procedure is the same as that described above in respect.

of the envelope, said photo cathode layer having'a surface areasufficiently large to accommodate the pattern, means for substantially uniformly illuminating saidphoto cath ode layer, means for supportingthe element producing the pattern outside the envelope and so close to said wall as to influence differentially the electron emission from; f

different points of the photo cathode layer in accordance with the pattern, and means for directing the electrons emitted from-the photocathode layer on to an electronsensitive surface which renders visiblethe pattern of the electron emission from said layer.

2. Arrangement as claimed in claim 1, comprising also a fluorescent screen within-said envelopeyand electron- The same is also true for the focus coil 24 (Fig. 10) with the associated source 'of current and adjustable resistance optical means for focussing the electron emission pattern from said photo cathode on to said fluorescent screen.

3. Method of making visible magnetic field or electric charge patterns, which consists in positioning the element producing the pattern in proximity to a photo-electric layer, flooding said layer with light of suitable wavelength to cause said layer to emit electrons in a distribution corresponding to the pattern, and accelerating and focuussing the emitted photoelectrons on to a luminous screen to produce on said screen a visible image of the electron emission of said layer.

4. An image converter tube, comprising an evacuated chamber the wall of which includes an electron-pervious portion, and a photo cathode having a photo-emissive area arranged in said evacuated chamber in a position facing said electron-pervious wall portion, the wall of said chamber further including a transparent portion so arranged as to permit a light image to be projected therethrough on to said photo cathode.

5. An image converter tube, comprising an evacuated chamber the wall of which includes an electron-pervious portion, a photo cathode having a photo-emissive area arranged in said evacuated chamber in a position. facing said electron-pervious wall portion, and means for imaging photo electrons emitted by said photo cathode" on to and throughjsaid electron-pervious wall portion, the wall of said chamber further including a transparent portion so arranged as to permit a light image to be projected therethrou'gh on to said photo cathode.

6. Apparatus for recording moving phenomena in the form of sequence of individual picture records on a tapelike carrier, comprising means for producing a stationary optical image representing said phenomena, a photocathode for converting said optical image into an electron image, means for scanning the electron image line by line through a gap, a plurality of collector anodes arranged side by side along the length of said gap for sub-dividing'each line of the electron image into image points, means for transmitting the output of the individual collector electrodes through amplifiers to the corresponding number of recording heads, said recording heads being arranged side by side, and means for continually feeding a tape-like magnetizable carrier past said array of recording heads whereby the image is recorded line by line on the carrier.

References Cited in the file of this patent UNlTED STATES PATENTS 1,771,360 Thurm July 22, 1930 1,974,911 Buecker et a1. Sept. 25, 1934 2,219,120 Somers Oct. 22, 1940 2,292,111 Farnsworth Aug. 4, 1942 2,307,728 Mertz Jan. 5, 1943 2,485,839 ODea Oct. 25, 1949 2,517,808 Sziklai Aug. 8, 1950 2,541,374 Morton Feb. 13, 1951 2,550,007 Fodor Apr. 24, 1951 2,572,494 Krieger et al. Oct. 23, 1951 2,575,570 Von Soden Nov. 20, 1951 2,591,977 Strutt et a1. Apr. 8, 1952 2,612,610 Marshall et a1 Sept. 30, 1952 2,657,378 Gray Oct. 27, 1953 2,716,154 Raibourn Aug. 23, 1955 

